1. Field of the Invention
The present invention relates to a heat treatment system, and more particularly, it relates to a heat treatment system which is employed for drying and baking protective resin layers of dip-coated electronic components, for example.
2. Description of the Background Art
FIG. 6 shows a holder W , called a separator, which is generally employed for dip-coating electronic components comprising plate-type lead terminals with protective resin. This holder W is adapted to hold a number of lead frames 51, to which electronic component elements 50 are mounted by soldering or the like, in parallel with each other. The holder W holding such lead frames 51 is so inverted as to dip the electronic component elements 50 in a dip-coating vessel, thereby forming protective resin layers 52 around the electronic component elements 50. Thereafter the holder W is carried toward a heat treating furnace, to dry and bake the protective resin layers 52.
In a conventional drying and baking step, a large-sized heat treating furnace of a batch system is employed for heat treating a number of holders at the same time. However, a waiting time is required for receiving the number of holders, which must be simultaneously introduced into the furnace, from a preceding step (dip-coating step), leading to inferior production efficiency. When pool means for temporarily storing such holders are provided in front and at the back of the furnace, it is possible to implement a continuous treating line thereby eliminating the waiting time. However, the capacity of each such pool means must correspond to at least the number of holders which can be simultaneously heat treated in the furnace. Thus, large spaces are required for installing such pool means, and much time is required for introducing the holders from the front pool means into the furnace and discharging the holders from the furnace to the back pool means.
In order to implement a continuous automatic treating line, as well as to simplify such operations for introducing and discharging the holders, it is possible to provide a conveyor type continuous heat treating furnace. The holders are continuously introduced into this furnace and moved therein upon a conveyor, to pass through a number of booths, with respective temperatures built in the furnace for a prescribed heat treatment.
However, since such a continuous heat treating furnace can obtain only a stepwise temperature profile, it is not suitable for the process of drying and baking protective resin layers, because a non-stepwise temperature increase profile is very important for this process. Moreover, when the line after the furnace is stopped for some reason, it is necessary to discharge all products which are contained in the furnace. Thus, a large pool means is required for storing such discharged products.